MEMS Fuel Injector

Technical Objectives

Northwest UAV Propulsion Systems (NWUAV) of McMinnville, Oregon, has funded the prototyping of a micro-nozzle fuel atomizer at the MBI using our low cost, laminated architecture. Atomization of fuels into a uniform distribution of small droplets can improve engine efficiency, thereby increasing the flight time for the unmanned air vehicles their engines are used in. NWUAV has acquired Microelectric Mechanical Systems (MEMS) fuel injection technology from Hewlett Packard that, coupled with MBI technology, can create a very small fuel injection device capable of sophisticated fuel delivery.

Results to Date

An annular design where the intake air passes through a center hole ringed with nozzles for fuel jetting was created. The fuel flow paths and nozzles are patterned into thin sheets of material that can then be stacked to achieve the needed fuel delivery throughput. As an example, a device may be as small as 3mm thick yet have 12,000 nozzles. Figure 1 below is a rendering of a fuel injector plate prototype and associated nozzle array.

Very short nozzles are necessary to keep the pressure drop low enough for MEM actuated droplet ejection. A combination of laser machining and micro-milling was used to demonstrate nozzle fabrication. Figure 2 shows the top and end views of an individual nozzle.

Video from a high speed camera was used to analyze droplet shape and size. The video clip below shows droplets ejected at 285Hz using piezo actuation.

Implications

ONAMI is funding a Gap project to develop a MEMS fuel injector for small aircraft engines. This same fuel injector can be used in consumer products such as lawnmowers, leaf blowers and chain saws. The improved combustion efficiency will reduce green house gas emissions.